The present invention relates to apparatus for increasing the dynamic range in an input stage of integrating type in an optoelectric receiver.
Two usual optical input stages are a transimpedance stage and an integrating stage. See, for example, the book Semiconductor Devices for Optical Communications, H. Kressel, Springer-Verlag, Berlin, Heidelberg, New York 1980. Integrating stages are better from the sensitivity aspect, since less noise is generated than in transimpedance stages. Since integrating stages easily become over driven they have, however, poorer dynamic properties than transimpedance stages.
To obtain high sensitivity in a receiver with an integrating input stage, it is sought to obtain low capacitance on its amplifier input. Low capacitance causes a high voltage on the amplifier input since the input signal is integrated. The input stage may therefore be over driven already at a moderate level of the input signal. An integrating stage is very sensitive for overamplification, since the signal information is in the derivative of the integrated signal.
Attempting to connect in extra capacitance electrically on the amplifier input to increase the dynamic range results in deteriorated sensitivity, due to unavoidable stray capacitances in the apparatus used for the connection.